This invention relates to a Schottky contact on a semiconductor surface and also to a method for the production thereof.
In the following there is to be understood by guard ring width the difference between the radius of the outer guard ring and the radius of the inner guard ring.
In the manufacture of Schottky contacts for radio-frequency uses one tries in general to minimize parasitic capacitances of the guard ring. This can be achieved, inter alia, by a small guard ring width. This requirement can be attained by self-aligning-techniques in the formation of the in guard ring.
From German Patent Application No. 31 24 572 a method is known for the production of Schottky diodes with a guard ring applied as self-aligning. By this method guard ring widths can be obtained which are less than or equal to one micrometer. In this known method, high-temperature steps are carried out before the application of the Schottky contact. Because the known method is not suitable for the manufacture of Schottky contacts, the ultimately applied Schottky contacts must not be exposed to additional high-temperature processes that may be necessary after completed Schottky metallization.
The method described in the mentioned German document No. 31 24 572 is also disclosed in the U.S. patent application bearing the Ser. No. 383,266, filed Mar. 28, 1982, and now matured into U.S. Pat. No. 4,481,041 on Nov. 6, 1984 abandoned.
Often radio-frequency Schottky diodes are to be exposed to high-temperature processes after application of the Schottky metallization.
It may be desirable to install Schottky diodes in a housing, whereby such diodes are subjected to installation temperatures of up to 620.degree. C. If, for example, two Schottky diodes are successively installed in such a housing one following the other, and if the two Schottky diodes are then exposed to different installation temperatures, the two Schottky diodes, if they have been manufactured according to prior art, will as a rule then have different parameters. If such housings, in which two Schottky diodes have been installed, are used for example in mixers, the two Schottky diodes installed in such a housing must have completely identical parameters also after their installation in this housing.
Also for achieving high reliability, High-Rel quality control, it becomes necessary to pre-age a Schottky contact at high temperatures of 500.degree. C.
Tempering between 400.degree. and 700.degree. C. is not possible with the Schottky contacts produced in the conventional manner for the reason that at these temperatures alkali impurities migrate from the contact metal into the insulator layer of the diodes, whereby the breakdown voltage of such diodes is reduced.
One attempt to remedy this deficiency is by coating all edges of the insulator material of the Schottky diodes with silicon nitride, by so-called edge sealing. However, to open the silicon nitride seal in the guard ring region requires a further photo/graphic processing, and this in turn results in an increase of the guard ring width, because in such a conventional method, where adjusting is done twice, the guard ring width must be at least double the greatest adjusting or alignment registration allowance.
While such edge sealing prevents alkali impurities from penetrating into the insulator layer of Schottky diodes during the planned tempering operations, it produces excessive parasitic capacitances of the guard ring due to its required rather large width which--as previously mentioned--are not acceptable for radio-frequency diodes.
The process disclosed in the previous referred to German patent application No. 31 24 575, which until now is being used for the production of ultrahigh frequency diodes with self-aligning guard ring, has low yields. In the conventional manufacturing process the Schottky metallization is variable, a fact which, in the manufacture of very many Schottky contacts, lead to asymmetries in the construction of these Schottky contacts in a large part of them and hence to relatively unfavorable electrical properties and hence to a relatively poor yield in the statistical average.
In Schottky metallization which tends to form silicide, this effect is intensified. Since in a Schottky contact according to prior art the guard ring region is normally not shielded, the distance between the oxide edge and the actual outer edge of the guard ring implant may easily be bridged upon formation of silicide.
Since in a Schottky contact with self-adjusted guard ring according to prior art the guard ring region is practically not shielded, after-treatments such a sputter etching, chemical etching, thermal oxidation, etc. on such a Schottky contact are useable to a very limited extent, because also in these after-treatments the distance between the oxide edge and the actual outer edge of the guard ring implant can easily be bridged.